The present invention relates to a continuous process for converting carotenoids, retinoids or natural colourants into finely divided pulverous forms which are particularly useful for coloring foodstuff and animal feeds.
Various processes have been described to prepare a powder containing the active ingredients with a crystallite size less than 1 micron. Most of the processes are well suited to batch processing applications.
For example, U.S. Pat. No. 3,998,753 describes a batch process for the preparation of a water dispersible carotenoid-containing powder, wherein the carotenoid powder has a particle size of less than 1 micron, which process comprises (a) forming a solution of a carotenoid and an antioxidant in a volatile solvent, said solvent being selected from the group consisting of halogenated aliphatic hydrocarbons such as chloroform, carbon tetra-chloride and methylene chloride; (b) forming an aqueous solution of sodium lauryl sulfate, a water soluble carrier composition such as e.g. gelatin, a preservative and a stabilizer, and adjusting said solution to a pH of about 10 to 11 and (c) forming an emulsion of the solutions of steps (a) and (b) by mixing at a high speed and high shear; removing the organic solvent and spray drying the resulting emulsion to obtain a carotenoid powder.
In the European Patent Publication EP-0065 193 B1 or the corresponding U.S. Pat. No. 4,522,743 a continuous process for the preparation of finely divided carotenoid powders is described, in which the carotenoid has a particle size essentially below 0.5 microns. The carotenoid is dissolved in a volatile, water miscible organic solvent within less than 10 sec. at 50-200xc2x0 C. The carotenoid is immediately precipitated in colloidally dispersed form from the resulting molecularly dispersed solution by rapid mixing with an aqueous solution of a swellable colloid at 0-50xc2x0 C. The preparation of the carotenoid solution and the precipitation of the carotenoid are effected continuously in two mixing chambers. The resulting dispersion is freed of solvent and the dispersing medium in a conventional manner.
However, for economical and ecological reasons this process has the disadvantage that a large amount of solvent must be used.
It is an object of the present invention to provide a process that overcomes the aforesaid drawback while converting the active ingredient into finely divided pulverous form.
The present invention is a process for preparing a pulverous preparation of a finely divided carotenoid, retinoid or natural colourant, which process comprises the steps of:
a) forming a suspension having an active ingredient which is taken from the group of carotenoids, retinoid and natural colourants, in a water-immiscible organic solvent optionally containing an antioxidant and/or an oil;
b) feeding the suspension of step a) to a heat exchanger;
c) heating said suspension to 100-250xc2x0 C., whereby the residence time in the heat exchanger is less than 5 sec to provide a solution;
d) rapidly mixing the solution of step c) with an aqueous solution of a swellable colloid such that the resulting mixture is at a temperature in the range of 20-100xc2x0 C.;
e) removing the organic solvent to provide a dispersion; and
f) converting the dispersion of step e) into a pulverous preparation;
where steps b) to f) are carried out continuously and in sequence.